NASA Satellites reveal major shifts in global freshwater

Rupali Pruthi

May 18, 2018 20:14 IST

NASA Satellites reveal major shifts in global freshwater

In a first, scientists have discovered that the Earth’s wet land areas are getting wetter and dry areas are getting drier due to various factors, including human water management, climate change and natural cycles.

The study was published on May 16, 2018 in the journal Nature.

Freshwater decline in India

Availability of freshwater has declined in the northern and eastern parts of India.

North India lost 19.2 gigatons of water every year during 2002-2016, while Central India witnessed increase in water storage levels, gaining 9.4 gigatons of water every year during the same period.

Areas in northern and eastern India, the Middle East, California and Australia are among the hotspots where overuse of water resources has caused a serious decline in the availability of freshwater.

Without corrective actions by the governments, the situation is likely to worsen in these areas.

Key Findings

• Freshwater is found in lakes, rivers, soil, snow, groundwater and ice. On land, freshwater is one of the most essential Earth's resources for drinking water and agriculture.

• The loss of freshwater from the ice sheets at the poles attributed to the climate change and indicates the rise in sea level.

• Though the water loss in some regions like the melting ice sheets and alpine glaciers is clearly driven by warming climate, however, it may take more time and data to determine the driving forces behind other patterns of freshwater change.

The Study

A team of scientists led by Matt Rodell of NASA’s Goddard Space Flight Centre came to know about the major shifts in the freshwater after studying the data of the NASA’s Earth-observing satellites.

The scientists used 14 years of data from the NASA’s twin Gravity Recovery and Climate Experiment (GRACE) satellites to track global trends in freshwater in 34 regions around the world.

They studied the data on human activities to trace the locations where freshwater is changing around the globe.

Map showing shifts in freshwater during 2002-2016

They scrutinised regions that have seen large increases or decreases in the total amount of freshwater, including water in lakes, rivers and water stored in underground aquifers, soil, snow and ice.

Through combined analysis of Global Precipitation Climatology Project, NASA’s Geological Survey Landsat imagery, irrigation maps and published reports of human activities, scientists were able to get a full understanding of the reasons for Earth’s freshwater changes.

Freshwater Trends witnessed in various regions

California: Pumping groundwater for agricultural uses is considered as a significant contributor to freshwater depletion, however, one should not forget that groundwater levels are also sensitive to cycles of persistent drought or rainy conditions.

This was the cause of the significant groundwater depletion observed in California’s Central Valley from 2007 to 2015. Southwestern California lost 4 gigatons of freshwater per year during the same period. A gigaton of water would fill 400,000 Olympic swimming pools.

Saudi Arabia: Downward trends in freshwater were also seen in Saudi Arabia, reflecting agricultural pressures. From 2002 to 2016, the region lost 6.1 gigatons per year of stored groundwater

Africa’s western Zambezi basin and Okavango Delta:The team also identified large trends in terrestrial freshwater storage that do not appear to be directly related to human activities, but the outcome of the natural cycles of high or low rainfall.

A perfect example is Africa’s western Zambezi basin and Okavango Delta, where water storage increased at an average rate of 29 gigatons per year from 2002 to 2016. This wet period followed at least two decades of dryness.

Xinjiang province in northwestern China: A combination of natural and human pressures led to complex scenarios in the Xinjiang province of northwestern China. During the first decades of this century, water declines occurred in Xinjiang, which lost 5.5 gigatons of terrestrial water storage per year.

This was caused by various factors such as additions to surface water from climate change-induced glacier melt, pumping of groundwater out of coal mines, depletions caused by increase in water consumption by irrigated cropland and evaporation of river water from the desert floor.

GRACE mission

• The twin GRACE satellites were launched in 2002 as a joint mission with the German Aerospace Centre (DLR).

• The two GRACE satellites -GRACE-1 and GRACE-2 - were launched from Plesetsk Cosmodrome, Russia on March 17, 2002.

• The satellites detected changes in Earth's gravity field caused by movements of mass on the planet below.

• Between 2002 and 2016, GRACE tracked the movement of freshwater around the planet.

• The data gathered from the satellites proved to be an important tool for studying Earth's ocean, geology and climate.

• The mission exceeded its initial 5-year target, operating for fifteen years until the decommissioning of GRACE-2 on October 27, 2017.

GRACE FO Mission: Next generation of Grace Mission

• The next generation of twin satellites called GRACE Follow-On (GRACE FO) is scheduled to be launched into the orbit from Vandenberg Air Force Base in California on May 22, 2018.

• GRACE-FO mission would be launched by NASA along with the German Research Centre for Geosciences.

• GRACE-FO will be launched to continue the original GRACE mission's legacy of tracking fluctuations in Earth's gravity field in order to detect changes in mass, including the mass of ice sheets and aquifers.

• Following this, NASA will be launching the Ice, Cloud, and land Elevation Satellite-2 (ICESat-2), which will use a highly advanced laser instrument to measure the changing elevation of ice around the world.

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